- DC bias on heater winding ? - 2 Updates
| John-Del <ohger1s@gmail.com>: Jul 28 01:26PM -0700 On Tuesday, July 28, 2020 at 7:44:42 AM UTC-4, Jeff Urban wrote: > You never know what kind of drugs these engineers are on. > I remember an RCA TV like a CTC211 or something, projection. They had a string of like seven transistors just to turn on the convergence subsystem. Why ? And it wasn't like there were a bunch of protection lines going to it, just a voltage and that's it. It was also not in the feedback loop. > I think they just want shit to be as hard to fix as possible. I think it's time to go back to A batteries.. |
| Phil Allison <pallison49@gmail.com>: Jul 28 08:07PM -0700 Jeff Urban wrote: ========================= > If the cathode is positive I can see why to put DC slightly higher on the filament. It will prevent any conduction I would think. However +70 is up there. What cathodes are at that high a positive voltage ? ** Marshalls all have cathode follower in the pre-amp where the the cathode is about 140V above ground. > I guess maybe for a common plate stage. (cathode follower) Perhaps a triode single phase splitter to drive push pull output tubes. ** Yep - about 90V above ground there too. > As far as getting rid of hum, you have to rectify that 70 volts, ** Derived from the HT so just two Rs and one small C. DC heater volts are used on many guitar amps and some hi-fi ones as well. .... Phil |
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